Differences

The younger Emmett Brown interacted with his older self by asking him for a wrench when he was working on his "weather experiment", although the younger Doc didn't realise he was talking to his older self.

Biff's gang discovers the older Marty McFly, and mistakes him for his younger self. They try to ambush him when he comes off of the stage, but the older Marty releases sandbags, knocking them out.

Marty retrieves the almanac and Biff's car is covered in manure again when Marty escapes thanks to the arrival of Doc in the flying DeLorean.

Doc is accidentally sent back to 1885 when the DeLorean is struck by lightning, and a temporal duplicate of the DeLorean is sent forward to 2025.